A liquid crystal display device has made rapid progress as a low power, thin and light-weighed display device in various fields. Particularly in recent years, a portable phone (cellular phone) also has made drastic progress and all types of portable phones employ the liquid crystal display device.
The liquid crystal display device employed in the portable phone is in many cases a reflective liquid crystal display device that is designed especially from the view point of low power consumption so that the life time of a battery is elongated. Furthermore, almost all of the reflective liquid crystal display devices are a transflective liquid crystal display device incorporating a backlight therein. The reason for this is that a liquid crystal display device is not a light-emitting display device and therefore, when the device is used under conditions with insufficient light intensity, i. e., under dark conditions, an image to be displayed on the device becomes difficult to view, thereby a backlight illumination is adopted to improve the visibility of an image to be displayed.
Additionally, as information communication using, for example e-mail, makes progress, a liquid crystal display screen also becomes large in size and accordingly, a portable phone becomes large in size. To address such problem, a portable phone has been developed which advantageously allows protection of the liquid crystal display screen and increase in portability.
A user of the portable phone usually carries the phone in a folded form and accordingly, every time when the user wants to know the current time or get information from display of incoming call, etc., the user needs to unfold the phone. To eliminate such inconvenience, a recent portable phone tends to be constructed so that a second liquid crystal panel is disposed independently of a first liquid crystal panel in a visible position when the portable phone is being folded, on which various types of information is always displayed.
In this case, since the first liquid crystal panel used when the portable phone is being unfolded and the second liquid crystal panel used when the portable phone is being folded both need to be used even under dark conditions, a transflective liquid crystal panel incorporating a backlight therein has been used.
FIG. 13 illustrates the exemplary configuration of a portable phone of the type conventionally used. The portable phone 1000 is constructed such that a main unit 1100 and a display unit 1200 are coupled together by a hinge 1300 so that the main unit 1100 and display unit 1200 are rotatable around the hinge 1300 and openable and closable relative to each other. Furthermore, the portable phone includes a key board 1109 provided on an upper surface of the main unit 1100 and is further constructed the display unit for a both-sided display such that a first liquid crystal display device 1101 and a second liquid crystal display device 1102 are disposed back to back in the display unit 1200.
The first liquid crystal display device 1101 comprises a first liquid crystal panel 1103 and a first backlight 1104, and the second liquid crystal display device 1102 comprises a second liquid crystal panel 1105 and a second backlight 1106. Moreover, a first windshield glass 1107 and a second windshield glass 1108 are provided on an internal (right side in the figure) surface and an external (left side in the figure) surface of a casing of the display unit 1200 to allow a user to view the liquid crystal panels 1103, 1105, respectively.
How the portable phone 1000 shown in FIG. 13 displays images will be explained below. When a user uses this portable phone 1000, the display unit 1200 folded toward the main unit 1100 is rotated in a direction of an arrow in the figure to open the portable phone. In this case, the liquid crystal panel 1103 of the first liquid crystal display device 1101 displays an image and the first backlight 1104 is turned on. At this point, the liquid crystal display panel 1105 of the second liquid crystal display device 1102 displays an image, but the second backlight 1106 is turned off. Therefore, the user operates the keyboard 1109 of the main unit 1100 while viewing display on the first liquid crystal display device 1101.
Thereafter, when the user of the portable phone 1000 uses it in a folded form, the display unit 1200 is folded by being rotated in the direction opposite the arrow to overlie the main unit 1100 and simultaneously, the display on the liquid crystal panel 1103 of the first liquid crystal display device 1101 is terminated, and the first backlight 1104 also is turned off. Then, the second backlight 1106 is turned on while the display on the liquid crystal panel 1105 of the second liquid crystal display device 1102 is continued. Note that the second backlight 1106 is turned off after a few tens seconds. Moreover, the second backlight 1106 is turned on, for example, when an incoming call is received or keypads are pressed by the user.
However, a problem arises in that two liquid crystal display devices are incorporated in the above-described conventional portable phone, causing increase in power consumption. Furthermore, each of the two liquid crystal display devices utilizes only the polarized component of light from a backlight, i.e., only the light transmitting through the polarizer of each of the display devices, meaning that the light utilization ratio of liquid crystal display device is 50% at the maximum. Since such a backlight is incorporated within each of the liquid crystal display devices, 50% of light from the backlight is absorbed, in other words, consumed away by the polarizer of each of the liquid crystal display devices. That is, to achieve desired intensity of light, the portable phone as described above dissipates twice the power as a portable phone with single liquid crystal display device.
Additionally, since the portable phone is configured to dispose two liquid crystal display devices so that the rear surfaces of the display devices face each other, the thickness of the display unit is increased, disadvantageously decreasing portability of the phone. For example, in case of the portable phone 1000 shown in FIG. 13, the liquid crystal panel 1103 of the first liquid crystal display device 1101 would have a thickness of 1.5 mm and the first backlight 1104 would have a thickness of 1 mm, meaning that the those two components would have a thickness totaling 2.5 mm. Since the second liquid crystal display device 1102 has the same structure as the first liquid crystal display device 1101, the first and second liquid crystal display devices have approximately the same thickness and when the two liquid crystal display devices are assembled in superimposed relation with back to back each other, the thickness of those display devices unfavorably becomes equal to about 5 mm. Additionally, when other necessary components such as a support frame are mounted to those display devices, the portable phone becomes very thick.
As described above, the conventional liquid crystal display device capable of displaying images on both sides includes some problems. That is, 50% or more of light from the backlight is consumed away and therefore, the portable phone disadvantageously dissipates twice the power as a portable phone with a single display, and further, the display unit of electronic equipments incorporating therein such conventional liquid crystal display device becomes thick, decreasing the portability of electronic equipments.